In the past, many on-highway trucks used mechanically controlled engines, which had mechanical governors and were mechanically connected with a throttle input. While these engines worked well, there were limitations in the variety of ways that the engine could be controlled. For example, timing and duration of fuel injection was typically controlled by the physical configuration of a cam shaft and the specific fuel injectors used on the engine. The timing and duration of fuel injection could be changed, but generally this required changing the mechanical components of the engine, such as a fuel injector or the camshaft. Electronically controlled engines greatly increased the flexibility of the fuel injection control for such engines. Using an electronically controlled fuel injector such as a HEUI fuel injector manufactured by the assignee of the present application, the controller can vary the timing and duration of fuel injected into the individual cylinders without changing the mechanical configuration of the engine. This permits the control system to vary timing and duration for different objectives, even while the engine is operating. For example, a control strategy could be developed to improve fuel economy while maintaining or improving emissions.
Other advantages of electronically controlled engines readily became apparent. Because the electronic control module could receive inputs from sensors and, to some extent, send signals to actuators on the vehicle and transmission, the engine's performance and operating characteristics could be adjusted based on sensed vehicle or transmission conditions. Many issued patents show examples of such integration. For example, U.S. Pat. No. 4,914,597, varies the engine power output based on whether cruise control is engaged or not. Another example is U.S. Pat. No. 4,493,303, issued to Mack Trucks Inc., varies the engine power output based on the transmission gear that is currently being used—the control allows the engine to produce greater power when the transmission is in one of the top two gears.
Still another example of the ability of electronically controlled engines to use signals from other systems is the use of distance sensing devices to influence the operations of the engine's cruise control system. As is known to those skilled in the art, conventional cruise control systems use various operator inputs to store a target cruise control vehicle speed, which is then typically used by the engine controller, along with other signals including vehicle speed, to calculate and generate a fuel command to minimize the error between the target cruise control vehicle speed and the actual vehicle speed. In this manner, the cruise control system controls the engine speed to maintain or control vehicle speed to the target speed. Advanced cruise control systems add additional capabilities to the conventional cruise control system. Typically an advanced cruise control system utilizes an electromagnetic beam, such as a laser beam, a microwave radar beam, or a video image, to determine the inter-vehicle distance and closure rate between the host vehicle and one or more forward vehicles. This information may then be used by the engine controller to automatically adapt to the traffic flow and “track” or follow the forward vehicle at a desired following distance selected by the operator. Distance and closure rate information may also be used to warn the vehicle operator of a potentially hazardous situation such as following the forward vehicle too closely for the current vehicle speed or approaching the forward vehicle or another object too rapidly such that a collision may occur. An example of an advanced cruise control system is disclosed in U.S. Pat. No. 6,076,622 issued to Eaton VORAD Technologies, LLC.
Oftentimes the advanced cruise control systems and engine control systems are manufactured by different companies. It is therefore important to have a standard communication format to permit these devices to communicate with various engine manufacturers' engine controllers. Standards, recommendations, guidelines, specifications, and the like, hereinafter collectively referred to as standards, are continually developed and published by various organizations. These standards designate component characteristics, testing procedures, communications formats, standards and methods of operation. Such organizations include the International Standards Organization (ISO), the Society of Automotive Engineers (SAE), and the Institute for Electrical and Electronics Engineers (IEEE), among numerous others. Often standards published by one organization will have corresponding designations in other organizations or may be a conglomeration of various other standards. Standards of particular interest in providing electronic engine control for vehicles such as heavy-duty tractor semitrailer vehicles are published by the SAE, one of which is designated SAE J1939. As is known, ISO 11898 is generally similar to and compatible with SAE J1939.
The J1939 standards define various control modes for electronically controlled engines including a normal mode, a cruise control mode, a torque control mode, and a speed and torque limit control mode. In normal mode, engine fueling is controlled based primarily on input received from the vehicle operator, typically via a throttle pedal. Of course a number of other factors influence the actual determination of engine fueling as described in greater detail below. In a standard cruise control mode, engine fueling is controlled to maintain a substantially constant engine speed. In torque control mode, a substantially constant engine output torque (as a percentage of total available torque) is effected regardless of engine speed and vehicle speed. Speed and torque limit control mode imposes an upper limit on engine speed and/or engine output torque. The override modes may be used to override the current operating mode and command the engine to a particular engine speed or engine output torque. The control mode is based on current operating conditions and commands received by the engine controller which may be generated by various other vehicle systems and subsystems or by the vehicle operator. A more detailed description of the modes of operation may be found in the J1939 specifications, the disclosures of which are hereby incorporated by reference in their entirety. Other, related standards utilized in electronic engine control and communication include SAE J1587, SAE J1708, and SAE J1843, the disclosures of which are also hereby incorporated by reference in their entirety.
As will be readily apparent to those skilled in the art, it is important for the engine controller to receive accurate data from the advanced cruise control system so that the engine controller, and particularly the cruise control, responds to vehicles or other detected obstacles. Although the data bus communications standards set forth in J1939 work satisfactorily, there are instances when too much data or noise on the bus, among other reasons, prevents the engine controller from receiving a particular data transmission, or causes the data to be corrupted. In prior art systems, the engine controller will simply disable the advanced cruise control system once an invalid data communication signal is received and causes the system to remain disabled until the engine controller has been re-initialized, which generally requires that the operator turn the ignition switch off, then re-start the engine. Although this system does help insure that the engine controller receives valid data from the advance cruise control system, it is inconvenient for the operator to have to re-initialize the controller for every invalid data transmission. It would be preferable to have a control system that overcomes these and other disadvantages associated with the prior art.